1. Field of the Invention
The present invention relates to a vehicular power transmission system provided with a transmission, the vehicular power transmission system shifting gear steps by a first shift clutch and a second shift clutch to which a power of an engine is transmitted.
2. Description of Background Art
There has been known a transmission of a vehicular power transmission system having a first shift clutch and a second shift clutch to which a power of an engine is transmitted, the shift clutches shifting gear steps (For instance, see JP-A No. 262163/1992, and JP-A No. 357267/2002).
A power of an engine is gradually transmitted to a transmission at start of a vehicle to relieve a start shock for smoothly starting the vehicle. When a fluid type torque converter is used for this, efficiency of power transmission in the torque converter is not always high, so that transmission loss can cause an increase in cost. In addition, when hydraulic clutches transmitting the power by friction of clutch plates are used as a first shift clutch and a second shift clutch which shift gear steps, the clutches are controlled to be in the partial clutch engagement state at start to relieve a start shock for permitting smooth start. The clutch plates causing a friction force are slidably contacted with each other to hasten exhaustion of the expensive hydraulic clutches.